1. Field of the Invention
The invention relates to a screwdriver, more particularly to a multi-purpose screwdriver that is convenient to use.
2. Description of the Related Art
A conventional screwdriver generally has a handle. One end of the handle is provided with a tool bit for driving a screw. In use, as the space in which the screwdriver works is often small and narrow, the user does not have enough room to manipulate the screwdriver smoothly. This need resulted in the development of a torsion screwdriver that can be turned in a single direction. Referring to FIG. 1, a conventional torsion screwdriver 1 is shown to include a hollow handle 11, a positioning sleeve 12 provided in the handle 11, a locking tube 13 received in the positioning sleeve 12, a plurality of locking cylinder rods 14 provided between the positioning sleeve 12 and the locking tube 13, a curved spring strip 15 provided on the locking tube 13, a rotary member 16 connected to the locking tube 13, and a bit-driving shaft 17 that can pass through all of the rotary member 16, the locking tube 13, and the positioning sleeve 12. The handle 11 has a hollow interior defining a receiving space 111 with a substantially square-shaped cross-section. One end of the handle 11 is closed by a screw cap 113. A packing ring 112 is used to ensure the closure effect. The positioning sleeve 12 has a front end provided with an inward projection 122, and a rear end formed with a through hole 121 for extension of a first end of the bit-driving shaft 17. There is further provided a retaining ring 18 on an outer side of the through hole 121 to secure the bit-driving shaft 17 onto the positioning sleeve 12. Furthermore, the locking tube 13 is generally cylindrical, and has a front end provided with an annular outward flange 133. The above-mentioned curved spring strip 15 and the rotary member 16 are positioned on the annular outward flange 133 of the locking tube 13. The curved spring strip 15 has a first end passing through the annular outward flange 133 of the locking tube 13 to be retained by the inward projection 122 of the positioning sleeve 12. The locking tube 13 further has an axially extending positioning hole 131, and a plurality of axially extending rod-retaining slots 132 for receiving the locking cylinder rods 14. The rod-retaining slots 132 are communicated with the positioning hole 131. In addition, the bit-driving shaft 17 has a second end provided with a tool bit receiving hole adapted to receive a tool bit 171.
Reference is made to FIG. 2, which shows the screwdriver 1 in a state of use. With cross-reference to FIG. 1, when the handle 11 is turned in a certain direction, the positioning sleeve 12 forces the locking cylinder rods 14 to abut against a peripheral surface of the bit-driving shaft 17, thereby bringing the bit-driving shaft 17 to turn with the handle 11. When the handle 11 is turned in a reverse direction, the positioning sleeve 12 ceases to force the locking cylinder rods 14 against the peripheral surface of the bit-driving shaft 17 so that the bit-driving shaft 17 does not turn with the handle 11. The intended object of unidirectional rotation can therefore be achieved. However, since the bit-driving shaft 17 always has the peripheral surface thereof in contact with the locking cylinder rods 14 regardless of its turning direction, it cannot be independently detached from the screwdriver 1. This is because removal of the bit-driving shaft 17 from the locking tube 13 will cause the locking cylinder rods 14 to fall into the positioning hole 131 of the locking tube 13. If the user intends to change the tool bit 171 at the second end of the bit-driving shaft 17 with another one (not shown) pre-disposed in the receiving space 111 of the handle 11, the user has to remove the screw cap 113 and the packing ring 112 in order to have access to the tool bit in the receiving space 111. After installing the new tool bit, the user has to put the previous tool bit in the receiving space 111, and then put the packing ring 112 and the screw cap 113 back into position. It can be seen that the conventional screwdriver 1 is very troublesome and inconvenient to use. In addition, the tool bit receiving hole of the bit-driving shaft 17 is adapted for use with tool bits of a single size only, thereby limiting the utility of the conventional screwdriver 1.